Selective expression of a progesterone receptor on the human sperm surface.

OBJECTIVE: To visualize progesterone (P) binding sites on the sperm surface, examine the relationship between hormone binding and hormone action (acrosome reaction), and determine the size of the hormone-responsive sperm subpopulation. DESIGN: Kinetic analysis of P binding was combined with the assessment of the hormone effect using a fluorescent acrosomal marker. SETTING: Private hospital, medical research center, and a university-based andrological laboratory. PATIENTS, PARTICIPANTS: Sperm samples were from healthy volunteers with normal spermiogram values. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Progesterone binding was analyzed by fluorescence microscopy and flow cytometry using P coupled to fluorescein isothiocyanate-labeled bovine serum albumin. Tetramethylrhodamine isothiocyanate-labeled Pisum sativum agglutinin was used as acrosomal marker in double-labeling experiments. RESULTS: After in vitro capacitation, only few spermatozoa (approximately 10%) were able to bind P to the cell surface, but most of these cells subsequently generated the acrosome reaction in response to hormone binding. CONCLUSIONS: The expression of P receptor sites on the human sperm surface is a major factor controlling the P-induced acrosome reaction. Further studies are warranted to explore if defective expression of the receptor can compromise fertility.     

溶脲脲原体感染与精子顶体反应

本实验对精液溶脲脲原体培养阳性的不育男性和其它不明原因不育男性及正常生育男性分别进行了精子明胶膜顶体反应和透射电镜观察。结果发现：在精液溶脲脲原体培养阳性的不育男性组中，严重感染者精子顶体反应率比其它不明原因不育组和正常生育男性组低，经统计学处理有显著意义（Ｐ１＜０．０１，Ｐ２＜０．０１）。电镜观察显示：溶脲脲原体感染者精子膜上有溶脲脲原体颗粒附着，出现精子膜和顶体膜缺损及破坏现象。本实验证实：溶脲脲原体感染可引起精子膜包括顶体膜的破损，精子顶体反应降低或消失。     

Effect of sperm-immobilizing antibodies on the acrosome reaction of human spermatozoa.

OBJECTIVE: To study by a triple stain technique the effect of sperm-immobilizing antibodies on the acrosome reaction of human spermatozoa. DESIGN: The spermatozoa were allowed to swim up and culture in a medium containing 7.5% (vol/vol) serum with sperm-immobilizing antibodies or control serum up to 6 hours. Sperm mobility was analyzed, and the percentage of live acrosome reacted spermatozoa was determined. SETTING: Samples were collected from patients referred to university hospital infertility clinics. MATERIALS: Serum samples were drawn from seven patients with sperm-immobilizing antibodies. All the sera were heat activated and stored at -40 degrees C until use. Semen samples were taken from two healthy donors. RESULTS: During culture for 6 hours, the percentage of live sperm showing the acrosome reaction increased significantly (P less than 0.01) in the control group but not in the sperm-immobilizing antibodies group. However, the inhibitory effect of sperm-immobilizing antibodies on the acrosome reaction was reversed when sperm was reincubated in medium with control serum (P less than 0.01). CONCLUSIONS: Sperm-immobilizing antibodies block fertilization at least in part by inhibiting the acrosome reaction of human spermatozoa.     

Acrosin activity as a potential marker for sperm membrane characteristics in unexplained male infertility

OBJECTIVE: To evaluate sperm membrane system integrity in unexplained infertile male subjects with three consecutive conception failures on IUI even though semen clinical parameters were normal. DESIGN: Prospective study. SETTING: Medical biotechnology laboratory, School of Medical Science and Technology IIT Kharagpur, India. PATIENT(S): Twenty-nine patients with unexplained infertility, 17 normal proven-fertile healthy donors, and 21 infertile males with low motility but with other semen parameters remaining normal. INTERVENTION(S): Semen samples were collected from unexplained infertile patients as well as from healthy fertile donors after abstinence of 3-5 days and were analyzed according to World Health Organization guidelines. MAIN OUTCOME MEASURE(S): Release of 5'-nucleotidase (plasma membrane marker), lactate dehydrogenase (mitochondrial marker) and free acrosin, proacrosin, and total acrosin (acrosomal membrane marker). RESULT(S): Plasma membrane integrity and respiratory activity of sperm cells were comparable in all three groups. The proacrosin-acrosin system was adversely affected in unexplained infertile subjects despite high sperm motility. CONCLUSION(S): Total acrosin activity may be considered as a sensitive biochemical marker for clinical evaluation of unexplained infertility in males.     

DNA strand breaks in human spermatozoa: a possible factor, to be considered in couples suffering from unexplained infertility.

BACKGROUND: The aim of this study was to assess the presence of DNA strand breaks and sperm cell morphology in men suffering from unexplained infertility, and to compare these results with normal fertile and oligozoospermic men. METHODS: One fresh sperm sample from proven fertile sperm donors (n=20) and from infertile men with oligozoospermia, (<20 x 10(6)/ml sperm cells) (n=74), and men suffering from unexplained infertility (>20 x 10(6)/ml sperm cells) (n=39) who delivered two sperm samples with 24 hours interval, were tested for the presence of DNA strand breaks in the spermatozoa by direct immunoperoxidase detection of digoxigenin-labeled genomic DNA. Correlations to other sperm parameters, sperm cell counts, motility, activation and Krüger's strict criteria were performed. RESULTS: DNA strand breaks in sperm cell nuclei were found significantly more often in sperm samples from men suffering from unexplained infertility compared to those from normal fertile men, and significantly more rarely compared with sperm samples from men with oligozoospermia. The percentages of normal spermatozoa (Krüger's strict criteria) were significantly lower in samples from men suffering from unexplained infertility compared to those of normal fertile men, but significantly higher compared to those of men with oligozoospermia. No difference was found between first and second day samples used for insemination, as regards DNA strand breaks, sperm cell morphology, total number of motile sperm cells, activation and motility degree. CONCLUSION: The present data suggest that a subgroup of men suffering from unexplained infertility have DNA strand breaks in their sperm cell DNA. This group might suffer from the same malfunction as many men with oligozoospermia, however, their apoptotic activated sites in the testis are different. Delivery of sperm samples with 24 hours interval does not affect any sperm cell counts, CASA, DNA strand breaks or morphology findings in sperm samples from men suffering from unexplained infertility.     

Receptors and channels regulating acrosome reactions

Prospective clinical studies informed by cloning and sequencing of sperm surface receptors and metal ion channels have elucidated critical early steps in the acrosome reaction that explain aspects of metal ion-related male infertility. Induction of the acrosome reaction is proposed to include non-nuclear progesterone receptor activation of Shaker-related sperm head voltage-gated potassium ion channels (VGKC). Men express VGKC isoforms with differing sensitivities to lead (Pb(2+)) inhibition, thus explaining interindividual variabilities in Pb(2+)-related male infertility. VGKC opening induces calcium (Ca(2+)) transients, and a signalling cascade induced by zona receptor aggregation requires an actin cytoskeleton created by the VGKC-induced Ca(2+) transients. Actin polymerization and stabilization, favoured by zinc (Zn(2+)) and depolymerized by cadmium (Cd(2+)), may mediate low Zn(2+) and high Cd(2+) infertile states. Zona receptor aggregation induces phosphotyrosine signals at sites, including sperm voltage-dependent Ca(2+) channels (VDCC), intermediate in electrophysiology between T- and L-type channels. Sperm surface VDCC localize at the sperm equatorial segment, the terminus of zona receptor translocation. Opening of VDCC admits a second Ca(2+) wave that activates phospholipase C phosphorylated in the zona receptor cascade. Phospholipase C induces fusogenic lipids and activates actin-severing proteins, depolymerizing the actin cytoskeleton and permitting apposition and fusion of acrosomal and plasma membranes.     

Analysis of aneuploidy in mini-percoll gradient centrifuged human sperm for intracytoplasmic sperm injection (ICSI) using fluorescence in situ hybridization

AIM: To study the aneuploidy rates of chromosomes 13, 18, 21, X and Y in Percoll gradient centrifuged sperm from infertile patients with male infertility factor treated by intracytoplasmic sperm injection (CSI) compared with healthy fertile donors and infertile patients with normal semen parameters. METHODS: This case-controlled study was conducted in a university hospital. Semen samples were obtained from three healthy fertile donors, eight infertile patients with normal semen parameters, and 18 infertile patients with male infertility factor. All samples were subjected to mini-Percoll gradient centrifugation before being processed through fluorescent in situ hybridization. The incidences of aneuploidy were compared using Chi-squared test. RESULTS AND CONCLUSIONS: A total of 64949 spermatozoa were analyzed. The disomy rates for chromosomes 13, 18, 21, and X or Y of sperm from patients with male infertility factor were 0.21%, 0.37%, 0.36% and 0.63%, respectively, whereas the diploidy rate was 0.17-0.23%. These incidences were higher than those from men with normal semen parameters. The result suggested that the embryos of patients with male infertility factor treated by ICSI are at increased risk of chromosome abnormalities.     

血管紧张素Ⅱ对人精子获能的影响

目的:探讨血管紧张素II(angiotensinII,AngII)对不育症精子获能的影响及其可能的作用方式。方法:不同浓度AngII与精子悬液共同孵育,以孕酮诱发顶体反应,采用FITC-PSA法测定细胞内Ca2+荧光强度来检测。结果:在未获能的精子悬液中AngII在10nmol/L和100nmol/L时均可明显加速精子获能和增强孕酮诱发的顶体反应(P<0.05),并可使细胞内Ca2+浓度升高(P<0.001),Losartan[AngII受体AT1(angiotensinIItype1receptor)拮抗剂]、EGTA可明显阻断和抑制这些过程。结论:AngII可以促进不育症精子获能,其结果可能是通过AT1受体介导,经改变精子细胞内Ca2+的浓度来实现。     

Modulation of human sperm function by peritoneal fluid

OBJECTIVE: To examine the effect of peritoneal fluid on various parameters of sperm function in vitro. DESIGN: Prospective study. SETTING: Basic research laboratory. PATIENT(S): Semen samples were obtained from normozoospermic volunteers (n = 43). Peritoneal fluids were aspirated laparoscopically from women with unexplained infertility (n = 14). Follicular fluid and oocytes were collected from patients undergoing IVF-ET. INTERVENTION(S): Sperm incubated under capacitating conditions were exposed to peritoneal fluid, and functional variables were evaluated in vitro. MAIN OUTCOME MEASURE(S): Sperm viability and motility, follicular fluid and calcium ionophore-induced acrosome reactions, protein tyrosine phosphorylation, expression of D-mannose binding sites, and ability of sperm to interact with zona pellucida. RESULT(S): Exposure of sperm to peritoneal fluid for up to 6 hours did not affect sperm viability or motility. Unlike follicular fluid, peritoneal fluid did not induce the acrosome reaction. Moreover, incubation of sperm with > or =20% v/v peritoneal fluid for 1 hour prevented the follicular fluid and the ionophore-induced acrosome reaction. Although treatment with peritoneal fluid allowed protein tyrosine phosphorylation during capacitation, it resulted in a significant decrease in the expression of D-mannose binding sites and sperm-zona pellucida binding. CONCLUSION(S): Peritoneal fluid maintains sperm survival and decreases sperm ability to respond to inducers of the acrosome reaction and bind to the zona pellucida in vitro, indicating that this fluid might modulate sperm function in vivo.     

Follicular fluid-induced acrosome reaction distinguishes a subgroup of men with unexplained infertility not identified by semen analysis

We compared the ability of sperm to undergo follicular fluid-induced acrosome reaction in vitro in fertile men and patients with unexplained infertility. After capacitation under optimum conditions, 28% of sperm from fertile men undergo acrosome reaction after follicular fluid exposure, whereas only 7% of the cells react spontaneously. In 15 men with unexplained infertility, 6 patients showed lack of acrosome reaction, whereas 9 men had sperm acrosome reactions similar to that of fertile men. However, in this cohort under study, semen characteristics of AR(+) and AR(-) patients were similar. In addition to inducing sperm acrosome reaction, follicular fluid also promoted significant changes in motion characteristics of capacitated sperm. Sperm curvilinear velocity (Vc) increased significantly after exposure to follicular fluid though linearity remained unchanged. The largest difference in cumulative Vc occurred at 90 microns/s. Assessing the ability of capacitated sperm to acrosome react may have clinical significance in predicting whether such sperm are capable of fertilizing an ovum.     

Direct effects of progesterone and antiprogesterone on human sperm hyperactivated motility and acrosome reaction.

OBJECTIVE: To study the direct effects of progesterone (P) and its antagonist RU486 (mifepristone) on sperm hyperactivation (HA) and acrosome reaction. DESIGN: Prospective evaluation of semen samples incubated in capacitation media with P and/or RU486. SETTING: University-affiliated tertiary care center. PATIENTS: Normal healthy volunteers. INTERVENTIONS: Semen samples were incubated in media with P or RU486 alone or in combination, and aliquots were taken at 10 minutes, 1, 5, and 24 hours for HA analyses by computer-aided sperm analysis system, and at 0, 5, and 24 hours for assessment of acrosome reaction by fluorescein-labeled Pisum sativum (pea) agglutinin. MAIN OUTCOME MEASURES: HA and acrosome reaction. RESULTS: Sperm HA was significantly increased at 10 minutes by P both at 10(-7) M (9.27 +/- 1.59%; mean +/- SEM) and 10(-6) M (9.39 +/- 1.94%) when compared with untreated spermatozoa (5.62 +/- 1.59%). The stimulatory effect of P on sperm HA was transient because this was not observed after 1, 5, and 24 hours of incubation. The antiprogesterone RU486 (10(-6) M) alone had no effect and did not abolish the stimulatory effect of P on HA. The %HA was further enhanced by the addition of RU486 at 10(-6) M to P at 10(-7) M (12.43 +/- 3.31%) or P at 10(-6) M (13.52 +/- 4.10%); however, this effect was not significantly different from P alone. Coincubation of P or RU486 with spermatozoa during capacitation did not stimulate the acrosome reaction in the concentrations tested. CONCLUSION: Progesterone directly stimulates human sperm HA transiently. Progesterone has no significant effect on acrosome reaction in capacitating spermatozoa. The effects of P are rapid and not counteracted by RU486, suggesting that the mechanism of action of P may not be mediated by specific P nuclear receptors.     

Sperm antibodies in men from infertile couples. Analysis of sperm agglutinins and immunofluorescent antibodies in 657 men.

Sera from 657 men from infertile couples were tested for sperm agglutinins and spermatozoal antibodies detectable by the indirect immunofluorescense technique (IFT), and the results were correlated to the clinical examinations of the couples. Sperm agglutinins were found in 6.7%. Spontaneous agglutination of the ejaculated spermatozoa was observed only among these men, most commonly among those with high serum titres. IF-antibodies against the four spermatozoal antigens located beneath the cell membrane occurred in 15.2% of the patients. Antibodies against the front part of the acrosome and the postnuclear cap were mainly IgM. Antibodies against the equatorial segment of the acrosome were predominantly IgG and in a few cases IgA, whereas straining of the main tail piece was caused by IgG antibodies. Considering the clinical fertility status of the couples, sperm agglutinins in high titres (greater than or equal to 10) against the equatorial segment and the main tail piece of the spermatozoa were found significantly more often among men from couples with unexplained infertility than among clinically normal men from couples where the findings in the women could be assumed to cause infertility. These results support the view that sperm agglutinins can cause infertility, whereas the significance of the IF-antibodies is still unclarified as, in some cases, these can be found even in high titres in men with proven fertility. The possible mechanism of autosensitization were evaluated by means of an anamnestic study.     

Gamma-aminobutyric acid (GABA) A and B receptors mediate the stimulatory effects of GABA on the human sperm acrosome reaction: interaction with progesterone

OBJECTIVE: To evaluate which gamma-aminobutyric acid (GABA) receptor mediates the stimulatory effects of this neurotransmitter on the human sperm acrosome reaction, and to examine the interaction of progesterone, a physiologic inducer of the acrosome reaction, with the GABA(A) receptor. DESIGN: Prospective study. SETTING: A university clinic of andrology. PATIENT(S): Men with normal sperm analysis parameters. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): The acrosome reaction of motile spermatozoa. RESULT(S): The acrosome reaction was stimulated by GABA in a dose-dependent manner. This effect was inhibited completely by bicuculline, a GABA(A) receptor antagonist, and only partially by saclofen, a GABA(B) receptor antagonist. Accordingly, muscimol, a GABA(A) receptor agonist, stimulated the acrosome reaction to the same extent as GABA, whereas baclofen, a GABA(B) receptor agonist, was less effective. Preincubation with progesterone followed by the addition of GABA resulted in a significant increase in the percentage of acrosome-reacted spermatozoa compared with progesterone alone. However, this increase was less than a simple addition of effects, suggesting that GABA and progesterone act through the same receptor and/or use the same mechanism of action. To test this hypothesis, the ability of progesterone to induce acrosome reaction was tested in the presence of bicuculline, which suppressed the stimulatory effects of progesterone. Given that the GABA(A) receptor is linked to the chloride channel, we tested whether picrotoxin, a blocker of this channel, could modulate the effects of progesterone or GABA. Picrotoxin completely suppressed the acrosome reaction induced by progesterone and only partially suppressed that caused by GABA. CONCLUSION(S): gamma-Aminobutyric acid stimulated the acrosome reaction in human spermatozoa, acting mainly through the GABA(A) receptor and to a lesser extent through the GABA(B) receptor. Progesterone interacted with the GABA(A) receptor to induce the acrosome reaction, and the functional integrity of the chloride channel was vital for this effect.     

Laurdan fluorescence: a simple method to evaluate sperm plasma membrane alterations

OBJECTIVE: To determine, by a simple fluorescence method, sperm plasma membrane alterations related with changes of lipid bilayer that, together with routine semen analysis, could help to elucidate the causes of the unexplained male infertility problems. DESIGN: Pilot study. SETTING: Andrology laboratory and biochemistry institute, medical school. PATIENT(S): Men whose semen was studied for infertility problems. INTERVENTIONS(s): No therapeutic intervention was performed on patients. MAIN OUTCOME MEASURE(S): Presence of spermatozoa plasma membrane alterations evidenced by evaluation of Laurdan fluorescence Generalized Polarization (GP) and reported as a function of increasing cell concentration, spermatozoa total motility, linear speed, and vitality. RESULT(S): Reporting GP values as a function of increasing sperm cell concentration, it is evident that the samples are distributed in two distinct areas: at >32 x 10(6) cells per milliliter, mean GP value was 0.303 +/- 0.015, whereas for lower sperm cell concentrations, the mean GP was 0.365 +/- 0.026 (P<.001). These data indicate that the spermatozoa plasma membranes are characterized by liquid-crystalline phases with different ordering degree and polarity and that about 50% of samples with normal semen characteristics (> or =20 x 10(6) cells per milliliter) show high GP values. CONCLUSION(S): Laurdan fluorescence can be used as a simple method to evaluate spermatozoa plasma membrane alterations, particularly in a group of infertile men presenting normal semen parameters. In these samples, Laurdan could be used as a simple tool for infertility assessment. In fact, it is known that compositional and physicochemical alterations of bilayer features can be important for the fertilizing ability of spermatozoa because they are necessary for a proper physiological membrane activity.     

Fertilization failure from a sperm chromatin defect in couples with unexplained infertility

OBJECTIVE: To investigate the relationship between unexplained infertility and fertilization failure from nucleoprotein defects in ejaculated human sperm and to study the usefulness of sperm chromatin assays, using AO fluorescence dye, to evaluate patients with unexplained infertility before treatment. STUDY DESIGN: From January 1999 to January 2000, 513 infertile couples had the clinical causes of their infertility assessed. During the next investigative period (February 2000-February 2001), 137 cases of unexplained infertility (n = 80) were chosen for this study, as were cases of tubal factor infertility (n = 57) as controls. The status of nuclear chromatin in ejaculated sperm was examined using acridine orange staining, followed by a conventional in vitro fertilization procedure. RESULTS: The number of patients with immature ejaculated sperm was 16 of 30 (53.3%) unexplained infertility cases involving fertilization failure, 8 of 50 (16.0%) unexplained infertility cases without fertilization failure and 5 of 57 (8.8%) tubal factor infertility cases. A significant difference was observed between unexplained infertility cases with fertilization failure and the other groups (P < .0001). CONCLUSION: These results suggest that the nuclear immaturity of ejaculated human sperm may be 1 of the primary factors underlying unexplained infertility.     

Influence of antisperm antibodies on the acrosome reaction as determined by flow cytometry

OBJECTIVE: To evaluate the influence of antisperm antibodies on the acrosome reaction (AR). DESIGN: Clinical study. SETTING: University of Marburg, Department of Andrology, Clinical Training Center of the European Academy of Andrology. PATIENT(S): Spermatozoa from a pool of healthy donors were incubated with 30 seminal plasma samples from infertile men containing antisperm antibodies; they were compared to a control group of 10 samples without antisperm antibodies and five samples with buffer only. INTERVENTION(S): The spontaneous acrosome reaction (SAR) and the induced acrosome reaction (IAR) by calcium ionophore A23187 were observed and determined by means of a flow cytometer. Flow cytometric double-staining estimates of acrosomal integrity were determined by using a monoclonal antibody (TUS 19), marked with a secondary fluorescein isothiocyanate-labeled antibody. Cell viability was determined by counterstaining with propidium iodide (PI). MAIN OUTCOME MEASURE(S): Number of acrosome reacted spermatozoa. RESULT(S): The spermatozoa treated with antisperm antibodies showed significantly higher SAR and IAR responses than the control group. CONCLUSION(S): Some of the antisperm antibodies from individual patients are able to enhance the acrosome reaction in donor sperm, but none of them appeared to inhibit acrosome reaction.     

Effect of antisperm sera on the acrosomal proteolytic activity in vitro

The effect of isoimmune antisperm sera from heifers and the effect of sera from cows and women with unexplained infertility were studied on the sperm acrosomal proteolytic activity (SAPA) of bull and human spermatozoa. All the sera were preliminarily tested by the method of Kibrick, and the cow sera were additionally tested by method of Isojima et al. Ejaculated bull and human spermatozoa were incubated in a medium containing antisera. SAPA was monitored on KODAK AR-10 autoradiographic plates according to Wendt et al. In some experiments the bull spermatozoa were preincubated in a medium containing 30% follicular fluid to induce capacitation and acrosomal reaction. The incubation of spermatozoa in isoimmune sera led to a marked inhibition of SAPA. A similar effect was observed when sera from cows and women with unexplained infertility were used. Preincubation of bull spermatozoa in follicular fluid intensified SAPA. The subsequent treatment with sera from infertile cows with high titres of spermagglutinins strongly inhibited this activity.     

人精子中芳香化酶表达与精子功能的关系

目的:研究精子细胞色素P450芳香化酶(P450arom)的表达及其与精子功能状态和受精力的关系。方法:以人精子穿透去透明带金黄地鼠卵异种体外受精试验(SPA)检测精子受精力;以三色法染色观察精子顶体反应(AR)的发生率。采用RT-PCR,用P450arom/GAPDH光密度值的比值代表P450arom的表达水平。结果:精子P450arom表达水平与受精率有一定的相关性(生育组r=0.5622;不育组r=0.6071)。正常男性与不明原因不育症患者精子P450arom/GAPDH比值分别为0.60±0.29,0.39±0.16,有显著差异(P<0.02)。P450arom表达水平与精子AR的发生率也有一定相关性(生育组r=0.5817;不育组r=0.5535)。结论:人精子中存在着P450arom表达产物;P450arom可能与精子功能有一定关系;P450arom表达异常可能与一些不明原因不育有关。     

γ－氨基丁酸诱发人精子顶体反应及其对若干离子转运影响的研究

本文用Ｌｅｃｔｉｎ染色法、原子吸收光谱法和电化学法研究了γ－氨基丁酸对人类精子顶体反应的诱导作用，以及它对Ｎａ＋、Ｋ＋、Ｃａ２＋、Ｍｇ２＋和Ｃｌ－在顶体反应时的转运情况的影响。结果表明：１．γ－氨基丁酸可明显地诱发人精子顶体反应（Ｐ＜０．０５）。２．γ－氨基丁酸可引起Ｎａ＋、Ｃａ２＋、Ｍｇ２＋内流，Ｋ＋外流和Ｃｌ－先外流再内流。因此，γ－氨基丁酸对人精子具有调控作用。     

The fertilization antigen-1 does not have proteolytic/acrosin activity, but its monoclonal antibody inhibits sperm capacitation and acrosome reaction.

OBJECTIVE: To determine if human sperm surface fertilization antigen exhibits proteolytic or acrosin activity and to investigate the mechanism(s) whereby monoclonal antibody (mAb) to fertilization antigen inhibits human sperm penetration of zona-free hamster ova. DESIGN: Proteolytic and acrosin activities of human fertilization antigen were determined. Acrosomal status, acrosin activity, and motion characteristics were evaluated after incubation of human sperm with immunoaffinity-purified mAb to fertilization antigen. SETTING: Academic research environment. PARTICIPANTS: Fertile donors used as controls for infertile patients for fertility evaluation. INTERVENTIONS: Human spermatozoa were treated with mAb to fertilization antigen and induced to undergo acrosome reaction using calcium ionophore A23187. MAIN OUTCOME MEASURES: Proteolytic and acrosin activities of fertilization antigen. Sperm penetration assay, acrosomal status, and motion parameters. RESULTS: Fertilization antigen does not exhibit proteolytic or acrosin activity; however, its mAb completely blocks human sperm penetration of zona-free hamster ova. The mAb to fertilization antigen inhibits ionophore-induced acrosome reaction and blocks development of the hyperactivated state of human sperm cells. CONCLUSIONS: Monoclonal antibody to fertilization antigen blocks fertilization by inhibiting capacitation and acrosome reaction.